Chemical composition of Leptocythere psammophila (Crustacea: Ostracoda) as influenced by winter metabolism and summer supplies

Leptocythere psammophila is well known for the ecophenotypic variations of the ornamentation of its carapace. To test the respective influences of the environmental parameters on its ornamentation, 41 living specimens were collected in the Baltic Sea, the North Sea and in the English Channel during spring, summer and winter (April 1987, September and December 1988). The carbonate carapaces of these specimens were analyzed by means of electron microprobe. Thirteen elements were detected. Statistical comparisons of means and variances were performed using classical F and t-tests. Data were submitted to Normalized Principal Component Analysis and Discriminant Analysis. There are no significant differences between chemical composition of the carapaces from the different stations. However, the variability of Baltic Sea specimens is lower than that of other stations. Nonetheless, strong and significant differences appear when samples are gathered by season. The chemical composition of summer individuals is controlled by variations in water salinity and in fine grain terrigenous sediment supply. The composition of winter samples is related to the incorporation of Mg. In the case of spring specimens, both these factors have to be considered. Discriminant analysis between winter and non-winter samples sets correctly 84% of the individuals. The wrongly classified specimens are interpreted as ostracods that did not molt during the season of sampling. By attributing them to their possible season of molting, the result of the Normalized Principal Component Analysis improves. Differences in ornamentation are slight. They occur between the samples from the Baltic Sea and those from the other stations. The former have larger and less numerous punctations and lack the smooth surface in the anteroventral part of the carapace. The punctation diameter is more variable during summer than during spring. In the range of environments investigated, ornamentation of the carapace of L. psammophila seems unaffected by the seasonal environmental variations whereas its composition exhibits strong differences.